Process and composition for removing residues from the microstructure of an object

ABSTRACT

A process for removing residues from the microstructure of an object is provided, which comprises steps of preparing a remover including carbon dioxide, an additive for removing the residues and a co-solvent dissolving the additive in said carbon dioxide at a pressurized fluid condition; and bringing the object into contact with the remover so as to remove the residues from the object. A composition for removing residues from the microstructure of an object is also provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process and a composition forremoving residues from the microstructure of an object. The presentinvention specifically relates to a process and a composition forremoving residues, such as resists, generated during a semiconductormanufacturing process from a semiconductor wafer surface having a finestructure of convex and concave portions.

[0003] 2. Description of the Related Art

[0004] It is required as one step in manufacturing a semiconductor waferto remove residues, such as photoresists, UV-hardened resists, X-rayhardened resists, ashed resists, carbon-fluorine containing polymer,plasma etch residues, and organic or inorganic contaminants from theother steps of the manufacturing process. The dry and wet removalmethods are commonly used In tie wet removal method, the semiconductorwafer is dipped in an agent, such as a water solution, including aremover to remove residues from the surface of semiconductor wafer.

[0005] Recently, supercritical carbon dioxide is used as such an agentbecause of its low viscosity and high diffusivity. According to suchproperties, cleaning with supercritical carbon dioxide provide severaladvances in the treatment of microstructures, such as high penetrationinto small areas between microstructures and successfully dryingmicrostructures because of non liquid-liquid interface in thesupercritical phase

[0006] However, supercritical carbon dioxide is not enough by itself toremove several residues from the surface of the semiconductor wafer. Toresolve this problem, several additives to supercritical carbon dioxideare proposed. As described in the Japanese unexamined patent publicationNo. 10-125644, methane or surfactant having CFx group is used as anadditive to supercritical carbon dioxide. In Japanese unexamined patentpublication No. 8-191063, dimethylsulfoxide or dimethyl-formamide isused as such an additive. However, based on the Inventors' studies,these additives are not always effective for removing residues.Especially, when the cleaning object is like a wafer which consist oflow dielectric constant materials, the quality of such wafer decreasedafter treatments by such process using alkaline compounds and water.This might be occurred because basic compounds and water caused damageson low dielectric constant materials, especially on materials havingdielectric constant lower than 4. (hereinafter referred to as low-kmaterials) Thus the present invention is objected to provide a novel andeffective cleaning without significant damage to the low-k materials.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is, therefore, to provide aprocess and a composition for effectively removing residues from themicrostructure of an object without significant damages to the low-kmaterials.

[0008] According to the present invention, a process is provided forremoving residues from the object, which comprises steps of preparing aremover including carbon dioxide, an additive for removing the residues,an inhibitor for protecting low-k damage and a co-solvent for dissolvingsaid additive in said carbon dioxide at a pressurized fluid condition,and bringing the object into contact with said remover so as to removethe residues from the object.

[0009] A composition is further provided for removing residue from theobject, which comprises carbon dioxide, a fluoride containing additive,a co-solvent or mixture of co-solvents capable of dissolving thefluoride containing additive, and an inhibitor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing and additional features and characteristics of thepresent invention will become more apparent from the following detaileddescription considered with reference to the accompanying drawings inwhich like reference numerals designate like elements and wherein:

[0011]FIG. 1 is a schematic diagram of an apparatus for removingresidues in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention is applied to the microstructure of anobject, e.g., a semiconductor wafer having a fine structure of convexand concave portions on its surface, and a substrate made of a metal,plastic or ceramic which forms or remains continuous or non-continuouslayer of materials different therefrom.

[0013] First, said remover used in this invention is described. Itincludes carbon dioxide, an additive for removing the residues, aninhibitor for suppressing residues and a co-solvent for dissolving saidadditive and said inhibitor in said carbon dioxide at a pressurizedfluid condition.

[0014] The pressurized carbon dioxide has a high dispersion rate andenables the dissolved residues to disperse therein. If carbon dioxide isconverted to a supercritical condition, it penetrates into fine patternportions of the object more effectively. By this feature, the additiveis conveyed into pores or concave portions on a surface of the objectdue to the low viscosity of carbon dioxide. The carbon dioxide ispressurized to 5 MPa or more, but not less than 7.1 MPa at a temperatureof 31° C. to convert the carbon dioxide to a supercritical fluidcondition.

[0015] Although any additives that can remove residues frommicrostructures could be used, it is preferred in the present inventionto use quaternaryammoniumfluorides because of their effective cleaningability. The preferred fluoride compounds includes at least one elementselected from the group consisting of tetramethylammoniumfluoride,tetraethylammoniumfluoride, tetrapropylammoniumfluoride,tetrabutylammoniumfluoride, cholinefluoride. Among these compounds,tetramethylammoniumfluoride (TMAF) is the most preferable one.

[0016] If the concentration of the additive is too low, cleaning ofresidues is not sufficient The lower limit of the additive is 0.001 wt%, preferably 0.005 wt %, and more preferably 0.01 wt %. However, whenthe concentration is more than 0.1 wt %, low-k materials are damagedbecause of excessive etching of low-k materials. Thus, the upper rangeof the additive is 0.1 wt %, preferably 0.05 wt %, and more preferably0.03 wt %.

[0017] The remover in the present invention also includespolyhydricalcohol. Polyhydric alcohol act as an inhibitor that protects the low-kmaterials from the significant damage from the additives such asfluorides. During inventors' studies, after some cleaning tests ofmicrostructures containing of low-k films, there were some liquid-likeresidues. These ‘liquid like residues’ were recognized as byproductsoriginated from etching reactions between some of the compounds in theremover and a part of low-k materials. Such byproducts could not beremoved and appeared as liquid-like residues because such products fromlow-k materials were not easily dissolved into supercritical carbondioxide.

[0018] By further investigations, it was found that the amount of suchliquid-like residues could be reduced when polyhydric alcohols were usedas a component of said remover. Therefore, the present invention, theremover includes polyhydric alcohols as an inhibitor to protect low-kmaterials from the damage. Although the mechanism of the protection oflow-k by polyhydric alcohol is still under investigations, polyhydricalcohol might adsorb on the surface of the low-k materials and protectthe surface from the attack of the chemicals.

[0019] Polyhydric alcohols may be dihydric alcohol such asethyleneglycol, propyleneglycol, trimethyleneglycol, diethyleneglycol,dipropyleneglycol, 1,2- , 1,3-, 1,4- or 2,3-butanediol,pentamehyleneglycol, hexyleneglycol, octyleneglycol or trihydricalcohols such as glycerin, trimethylolpropanae, 1,2,6-hexanetriol, andtetrahydric alcohols such as pentaelythritol. Also, polyethyleneglycolor polypropyleneglycol may be used. Among, these compounds, dihydricalcohols are preferable and ethyleneglycol and propyleneglycol are morepreferable.

[0020] If the concentration of the polyhydric alcohols is too low, theprotection of the low-k is not sufficient and amount of liquid-likeresidues increases. The lower range of the polyhydric alcohols is 0.005wt %, preferably 0.007 wt %, and more preferably 0.01 wt %. However,when the concentration is higher than 0.1 wt %, the efficiency of theprotection is saturated. Thus, the upper range of the polyhydricalocholos is 0.1 wt %, preferably 0.07 wt %, and more preferably 0.05 wt%.

[0021] As the pressurzed carbon dioxide is not enough by itself todissolve additives and inhibitors such as TMAF and polyhydric alcohols,the present invention uses co-solvent to dissolve them into carbondioxide. The co-solvent of the present invention is a compound having anaffinity to both carbon dioxide and the additive. Such a co-solventdissolves or disperses the additive homogeneously in the pressurizedcarbon dioxidein fluid condition. Although any co-solvent is used if itcan make additives and polyhydric alcohols soluble into pressurizedcarbon dioxide, alcohols are preferable. The alcohol may be any alcohol,e.g. ethanol, methanol, n-propanol, iso-propanol, n-butanol,iso-butanol, diethyleneglycolmonomethyleter,diethyleneglycolmonoethyleter, and hexafluoro isopropanol. Among thesealcohols, methanol ethanol and iso-propanol are preferable because theyact as a good co-solvent to wide range of compounds.

[0022] The kind and amount of the co-solvent are selected depending onthe kind and amount of the additive to carbon dioxide. The amount of theco-solvent is preferably five times or more than that of the additivebecause the remover easily becomes homogeneous and transparent.Alternatively, the remover may include the co-solvent in a range of 1wt. % to 50 wt. %. If more than 50 wt. % of the co-solvent is added, thepenetration rate of the remover decreases due to less amount of carbondioxide. It is prefrable to use a remover including carbon dioxide,alcohol as the co-solvent, quaternaryammoniumfluoride and/orquaternaryammoniumhydroxide as the additive because these additives arewell dissolved in carbon dioxide by alcohol and are CQ philic.

[0023] When TMAF is used as an additive, TMAF should be initiallydissolved into said co-solvent because TMAF is a sold at ambienttemperature. At this time, solvents such as dimethylacetamide (DMAC) orde-ionized water (DIW) could be added to help TMAF to be dissolved intocarbon dioxide more easily. The amount of such solvents is preferablyless than 20 times of TMAF. Especially, a concentration of DIW should beminimized because of the damages to the low-k materials.

[0024] The practical procedure will be described using drawings. In thebelow description, components of remover other than carbon dioxide, amixture of additives, inhibitors, co-solvents is simply called ‘cleaningreagents’. FIG. 1 shows a simplified schematic drawing of an apparatususe for removing residues according to the present invention. In thefigure, 1 is a carbon dioxide cylinder, 2 is a high pressure pump forcarbon dioxide, 3 is a storage tank of cleaning reagents, 4 is a pumpfor cleaning reagents, 5 is a valve, 6 is a storage tank for rinsereagents, 7 is a pump for rinse reagents, 8 is a valve, 9 is a highpressure vessel, and 10 is a thermostat. Firstly, the microstructures,for example, semiconductor wafer having residues on its surface isintroduced to and placed in a high pressure vessel 9, then carbondioxide is supplied from a carbon dioxide cylinder 1 to the highpressure vessel 9 by a high pressure pump 2. The high pressure vessel 9is thermostated at a specific temperature by a thermostat 10 in order tomaintain the pressurized carbon dioxide in the high pressure vessel 9 atthe supercritical condition. High pressure vessel 9 can be replaced bythat having heating unit. Cleaning reagents are supplied to the highpressure vessel 9 from tanks 3 by high pressure pumps 4. Cleaning stepstarts at the time when the cleaning reagents are fed from tank 3 to thehigh pressure vessel 9. The feed of the carbon dioxide and cleaningreagents may be continuous or batch-like.

[0025] The removing process is performed at a temperature in the rangefrom 31° C. to 120° C., and at a pressure ranged from 5 M Pa to 30 M Pa,preferably, from 7.1 M Pa to 20 M Pa. The time required for removing theresidues depends on the size of the object, the kind and amount of theresidues, which is usually in the range from a minute to several tenminutes.

[0026] After a cleaning step, a rinse step follows. Residues removedfrom surface during the cleaning step remains in the vessel 9 after thecleaning step finishes. If pure carbon dioxide is fed into suchconditions, some portion of residues will deposit on the surface of theobjects. Therefore, after the cleaning step, the first rinse step withthe mixture of carbon dioxide and rinse agents is applied. After thisfirst rinse step, the second rinse step with pure carbon dioxide isapplied.

[0027] Preferable rinse agents used in the first rinse step are thosethat can remove liquid-like residues. After inventors' investigations,compounds having specific dielectric constant similar to water areeffective for this purpose. Since the specific dielectric constant ofwater is 78 at 25° C. under atmospheric pressure, compounds havingspecific dielectric constant not smaller than 78 are used. The reasonwhy the required specific dielectric constants are similar to that ofwater is that the liquid-like residues as byproducts of low-k etchinghave high polarity, resulting in the high affinity to the polarsolvents.

[0028] On the other hand, polyhydric alcohols are required in thepresent invention as described in the previous section. However, if theamount of the cleaning reagents is small enough to suppress theby-production due to damages of low-k materials, rinse agent havingspecific dielectric constant not smaller than 78 may be used with arelative longer treatment time without any addition of polyhydricalcohols in the cleaning step. However, in order to minimize the processtime of the first rinse step (for example, 5 min. or less), it ispreferable to minimize the by-production of liquid-like residues withaddition of polyhydric alcohols.

[0029] Practically, the first rinse step can be done by stopping thefeed of the cleaning reagents by the valve 5, followed by feed of carbondioxide and rinse reagents to the high pressure vessel 9 to get rid ofthe contents of vessel 9. A flow meter 12 may be used to control theflow rate. During the first rinse step, it is preferable to decrease thefeed rate of rinse reagents gradually or in a stepwise manner with valve8 to replace the contents by pure carbon dioxide, followed by the secondrinse step with pure carbon dioxide.

[0030] Fluid evacuated from the cleaning step and the first rinse stepcan be recycled and reused by the separation into gaseous carbon dioxideand liquid fractions by a carbon dioxide recycle process, for example,including a liquid gas separator.

[0031] After the second rinse step, by releasing pressure with apressure control valve 11, carbon dioxide vaporize to gaseous phase.Therefore, microstructures such as semiconductor wafers can be driedwithout any water mark and any destructions of the pattern.

[0032] Hereinafter, the present invention is described with reference toexperiments. Although the present invention has been fully described byway of example with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, theyshould be construed as being included therein.

EXAMPLES Example 1

[0033] At first, in order to investigate the degree of the damage ofcleaning reagent to the low-k materials, etch rate measurements of low-kfilms were carried out. Low-k films were prepared on the silicon waferby coating the materials consisting of organic silicon followed byheating and drying. The film thickness of the low-k films was about 5000Å and k-value was in the range of 2 to 3. Using cleaning tools shown inthe FIG. 1, a wafer coated by the low-k film was set into the highpressure vessel 9. After closing the cover of the vessel 9, carbondioxide was introduced from carbon dioxide cylinder 1 through the pump2. The temperature of the vessel 9 was maintained at 50° C. with athermostat 10 and the pressure was controlled by the control valve 11.After the pressure reached 15 MPa, cleaning reagents were fed into thevessel 9 from the storage tank 4 through the pump 4. After a 10minute-treatment, 5 minutes of the first rinse step was applied,followed by 10 minutes of the second rinse step with a pure carbondioxide. A rinse reagent used in the first rinse step was 0.5wt % ofde-ionized water, 4.5 wt % of ethanol and 95 wt % of carbon dioxide.

[0034] After the second rinse step, the pressure was released by thepressure control valve 11 and wafer was taken to be provided for furtherevaluation. Etch rates (Å/min) were calculated by the difference in thefilm thickness before and after the treatment divided by the 10 min.Film thickness was measured by an optical measurement tool. The resultsare shown in table 1.

[0035] The abbreviation used in table 1 are follows;

[0036] TMAF: Tetramethylammoniumfluoride, DMAC: Dimethylacetamide, DIW:de-ionized water, EG: Ethyleneglycol, PG: Propyleneglycol, EtOH: EthanolTABLE 1 Componets of remover Co- Addtional Etch Additive and inhibitorsolvent solvents rate — CO₂ TMAF EG PG EtOH DMAC DIW Å/min 1 95 0.013 00 4.9 0.063 0.024 240 2 95 0.013 0.012 0 4.9 0.051 0.024 230 3 95 0.0130 0.012 4.9 0.063 0.024 155 4 95 0.013 0 0.024 4.9 0.051 0.024 148 5 950.005 0 0 5.1 0.066 0 53 6 95 0.005 0 0.012 4.9 0.054 0 19 7 95 0.013 00 4.8 0.165 0 91 8 95 0.013 0 0.03 4.8 0.135 0 67

Example 2

[0037] In the same manner described in the example 1, wafers coated bythe low-k film were prepared. After line and space patterns (180 nmwidth) were processed by the lithography on the surface, ordinaryetching by fluorocarbon gases and ashing by oxygen plasma. After oneminute cleaning with cleaning reagents listed in the table 2 under thesame condition as the example 1, five minute or ten minute of the firstrinse step using components listed in table 2, followed by ten minutesof the second rinse step with a pure carbon dioxide. The first rinsereagents used were 0.5 wt % of listed components, 4.5 wt % of ethanoland 95 wt % of carbon dioxide. After the release of the pressure byopening the pressure control valve 11, the imated wafer was taken andprovided for the evaluation. The cleaning performance was evaluated bythe observation of a scanning electron microscope (SEM) with amplitudeof 50000. The performance was checked both residues on the surface ofthe line and the liquid-like residues. The criteria used forinvestigation was as follows;

[0038] Excellent: No residues remained

[0039] Good: Amount of residues was less than 1 area % on the patternedside of the wafer.

[0040] NG (Not good: Amount of residues was more than 1 area %.

[0041] The abbreviation used in table 2 are follows;

[0042] TMAF: Tetramethylammoniumfluoride, DMAC: Dimethylacetamide, H₂O:water (ε=78), DIW: de-ionized water, EG: Ethyleneglycol, PG:Propyleneglycol, EtOH: Ethanol, FA: Formamide (ε=111), MF:Methylformamide (ε=182), DMF: Dimethylformamide (ε=36.7), MeOH: Methanol(ε=42), AC: Acetone (ε=21)

[0043] According to the cleaning process described in the presentinvention, low-k materials that are easily damaged by the cleaningreagents could be protected by the use of the cleaning reagentsincluding inhibitors such as polyhydric alcohols added into carbondioxide. Besides, residues produced because of the damages of low-kmaterials by the cleaning reagents could be removed by a suitableselection of the rinse reagents. Therefore, the cleaning processdescribed in the present invention provide one of the optimized cleaningprocesses applicable to the microstructure such as semiconductor wafers.TABLE 2 Components of remover Co- Additional 1 min cleaning + 1 mincleaning + Run Additive and inhibitor solvent solvents 5 min 1st rinse10 min 1st rinse — CO₂ TMAF EG PG EtOH DMAC DIW Rinse liquid-likepolymer liquid-like polymer 1 95 0.013 0 0 4.9 0.063 0.024 DMF NGExcellent NG Excellent 2 95 0.013 0 0 4.9 0.063 0.024 MeOH NG ExcellentNG Excellent 3 95 0.013 0 0 4.9 0.063 0.024 AC NG Excellent NG Excdllenl4 95 0.013 0 0 4.9 0.063 0.024 H₂O NC Excellent Excellent Excellent 5 950.013 0 0 4.9 0.063 0.024 FA Excellent Excellent Excellent Excellent 695 0.013 0 0 4.9 0.063 0.024 MF Excellent Excellent Excellent Excellent7 95 0.013 0.012 0 4.9 0.051 0.024 H₂O NG Excellent Excellent Excellent8 95 0.013 0 0.012 4.9 0.063 0.024 H₂O Good Excellent ExcellentExcellent 9 95 0.013 0 0.012 4.9 0.063 0.024 FA Excellent ExcellentExcellent Exccllent 10 95 0.013 0 0.024 4.9 0.051 0.024 H₂O ExcellentExcellent Excellent Excellent 11 95 0.005 0 0 5.1 0.066 0 H₂O Good GoodExcellent Good 12 95 0.005 0 0.012 4.9 0.054 0 H₂O Excellent GoodExcellent Good 13 95 0.013 0 0 4.8 0.165 0 H₂O Good Excellent ExcellentExccllent 14 95 0.013 0 0 4.8 0.165 0 FA Excellent Excellent ExcellentExcellent 15 95 0.013 0 0.03 4.8 0.135 0 H₂O Excellent ExcellentExcellent Excellent

What is claimed is:
 1. A process for removing residues from themicrostructure of an object comprising steps of: preparing a removerincluding carbon dioxide, an additive for removing the residues, aninhibitor for suppressing residues and a co-solvent for dissolving saidadditive and said inhibitor in said carbon dioxide at a pressurizedfluid condition; and bringing the object into contact with said removerso as to remove the residues from the object.
 2. The process accordingto claim 1, wherein said additive includes quaternaryammoniumfluoride.3. The process according to claim 1, wherein said additive includestetramethylammoniumfluoride.
 4. The process according to claim 1,wherein the concentration of said additive is between 0.001 to 0.1weight percent.
 5. The process according to claim 1, wherein saidinhibitor includes polyhydric alcohol.
 6. The process according to claim5, wherein said polyhydric alcohol is a dihydric alcohol.
 7. The processaccording to claim 5, wherein said dihydric alcohol is a propyleneglycol.
 8. A process for removing residues from the microstructure of anobject comprising steps of: preparing a remover including carbondioxide, an additive for removing the residues and a co-solvent fordissolving said additive in said carbon dioxide at a pressurized fluidcondition; and bringing the object into contact with said remover so asto remove the residues from the object followed by a rinse stepincluding rinse agent of which dielectric constant at a temperature andpressure of 25° C. and 1 at m is 78 or larger.
 9. The process accordingto claim 8, wherein said rinse agent is selected from at least one ofthe compounds including water, formamide, methylformamide andmethylacetamide.
 10. The process according to claim 8, wherein saidremover includes an inhibitor for suppressing residues.
 11. The processaccording to claim 8, wherein said additive includesquaternaryammoniumfluoride.
 12. The process according to claim 8,wherein said additive includes tetramethylammoniumfluoride.
 13. Theprocess according to claim 8, wherein the concentration of said additiveis between 0.001 to 0.1 weight percent.
 14. The process according toclaim 10, wherein said inhibitor includes polyhydric alcohol.
 15. Theprocess according to claim 14, wherein said polyhydric alcohol is adihydric alcohol.
 16. The process according to claim 14, wherein saiddihydric alcohol is a propylene glycol.
 17. A composition for removingresidue from the microstructure of an object, comprising: carbondioxide, a fluoride containing additive, a co-solvent or mixture ofco-solvents capable of dissolving the fluoride containing additive, andan inhibitor.
 18. The composition according to claim 17, wherein thefluoride containing additive is a quaternary ammonium fluoride.
 19. Thecomposition according to claim 18, wherein the quaternary ammoniumfluoride is tetramethylammonium fluoride.
 20. The composition accordingto claim 17, wherein the co-solvent or mixture of co-solvents isethanol, methanol, n-propanol, isopropanol, n-butanol ordimethylacetamide.
 21. The composition according to claim 20, whereinthe co-solvent is a mixture of ethanol and dimethylacetamide.
 22. Thecomposition according to claim 17, wherein the inhibitor is propyleneglycol.
 23. A composition for removing residue from the microstructureof an object, comprising: carbon dioxide, tetramethylammoniumfluoride,ethanol, dimethylacetamide, and propylene glycol.